History of the Atom - By Sally Chen

Aristotle

- Democritus:  suggested that the differences between substances were the direct result of differences in the size and shape of tiny, uniform, unbreakable particles.

- Aristotle:  4 basic elements:  water, air, fire and earth.

- Antoine Lavoisier:  created the first law of the conservation of mass.

- John Dalton:  created Dalton’s Atomic Theory, which is a combination of all discoveries about atoms.
- J. J. Thomson:  He discovered the existence of electron in 1897.  He found it was about 2000 times less than the mass of hydrogen.

- Ernest Rutherford:  He discovered the atomic nucleus and presumed the nuclear structure of the atom and predicted the existence of the neutron.

- Robert Millikan:  He accurately determined the charge carried by an electron, using “falling-drop method”.  He also demonstrated that this quantity was a constant for all electrons.

- Marie Curie:  She and her husband Pierre Curie isolated the elements polonium and radium.  She also developed methods for the separation of radium from radioactive residues.

Albert Einstein

- James Chadwick:  He discovered the neutron, and that it had about the same mass as a hydrogen atom.

- Max Planck:  He discovered that light was released by heat sources in a particular pattern of frequencies for different elements.  Each frequency of light corresponded to different sets of colors of lights seen by our eyes (lowest to highest:  red, orange, yellow, green, blue, purple, and violet).

- Albert Einstein:  In 1905 Einstein projected a theory that light was made up of localized particles.  He also defined detailed equations on light wavelengths and frequency differences within the same light.  He named packets of light energy photons.  Einstein believed that each atom oscillates independently instead of joining to others.

Joseph Louis Proust

- Niels Bohr:  electric fields between negatively charged electrons and a positively charged nucleus must hold electrons in their orbits.  He thought that electrons could circle at different orbit levels above the nucleus depending on how much energy they had.  When electrons jumped to lower levels, Bohr suggested that energy would be released as light.  The diagram of his version of atom is called the Bohr Diagram.

- Louis De Broglie:  He discovered the wave nature of electrons.  He had a theory that the behavior of the electron could also be better understood not just as a particle, but as both a particle and a wave.

- Erwin Schrodinger:  He created an equation describing how Broglie’s theory would be possible, not only for atoms and parts of the atom, but even for large objects – maybe even for the entire universe.

- Joseph Louis Proust:  He discovered the law of definite proportions, also known as Proust’s law, which states that chemical compounds always have the same fraction of each element in them by mass.

- Henri Becquerel:  He was the first person who discovered radiation.

History of Periodic Table--Nemo Jin

Long time ago, a group of people believed that they could turn metals into pure gold. These people were called alchemists. Although they were not successful, many different elements were discovered by these alchemists, including gold, silver, tin, copper, lead and mercury. However, the first scientific discovery of an element was in 1649, the discovery of phosphorous by Hennig Brand.

In the next 200 years, a total of 63 elements had been discovered, and scientists began to recognize patterns in properties and began to develop classification schemes.


In 1863, John Newlands, a English chemist divided 56 elements into 11 groups, based on their characteristics. He also proposed the Law of Octaves,which stated that any given element will exhibit analogous behavior to the eighth element following it in the table.

                                             (John Newlands' Periodic Table)

(Meyer's 1864 textbook included a rather abbreviated version of a periodic table used to classify the elements, but unfortunately for Meyer, Mendeleev's table was the first one available to the scientific community)


      “Father of Periodic Table"
In 1869, Russian chemist Dimitri Mendeleev arranged chemical elements by their atomic masses.  He also accurately predicted the properties of some undiscovered elements, leaving spaces open in his periodic table for them. His contribution to the development of periodic table was usually considered as the foundation of modern periodic table. 

In 1894, Sir William Ramsay and Lord Rayleigh discovered the noble gases which did not fit any of the known periodic groups. Because of the zero valency of the elements, noble gases were added to the periodic table as group 0

In 1911, A. van den Broek proposed that the atomic weight of an element was approximately equal to the charge on an atom. This charge, later termed the atomic number, could be used to number the elements within the periodic table.

The last major changes to the periodic table was in the middle of the 20th Century.


Glenn Seaborg 
--discovery of elements from 94 to 102 
--rearrangement of the periodic table (placing the actinide series below the lanthanide series) 
He was awarded the Nobel Prize in chemistry for his work. Element 106 has been named seaborgium (Sg) in his honor.